Orion is built on Safari's browser engine (WebKit) and can thus import cookies from Safari:
https://help.kagi.com/orion/getting-started/importing.html
It doesn't state it explicitly for cookies, but Orion's faq does say that they import Safari Passwords at install time, so they likely import all the Safari data as a starting point: https://kagi.com/orion/faq.html#passwords
Its most likely that this isn't your browsers doing, but in this case ebay. It successfully recognised your computer by matching your configuration, ip, and browser engine and thus was able to present you with a familiar experience^tm^.
Orion actually goes out of its way to block fingerprinting by default, this is most likely it importing Safari data as a starting point since it's also WebKit based.
IMO It's practically impossible to "block" fingerprinting, as anything that you do block can be tested for and used against you as yet another data point for your fingerprint. You can even fingerprint someone by TLS alone, no html/css/js needed, which CloudFlare uses on a massive scale to great success, unfortunately.
Even anti-fingerprint tactics that use fake/random/lying data can also be tested for (if nothing else heuristically), which tools like creepjs absolutely do make use of and it can accurately detect most such techniques.
It's terrifying how effective user tracking is today, and I think most people are really unaware of how extensive it is.
Prof. Jennifer Golbeck explains it well (for non-technical folks) in "Taking Control of Your Personal Data" published by The Teaching Company, ISBN:978-1629978390, likely available at your local library as a DVD or streaming. (I know that sounds like an ad, she just explains things so well I hope more non-technical people will see it).
My library doesn't even have a single computer-related book :(
This seems plausible so I tried other browsers and computers on my network.
Edge, Firefox, Brave, Arc, and DuckDuckGo all showed the same page on Ebay with "Trending in Sneakers" and "Trending in Watches". I was searching for sneakers recently but not watches.
Orion is the only one that showed "Your Recently Viewed Items" with specific items I was looking at in Safari. I went ahead and chose "Reset Orion" from the menu and see it's now operating the same as the other browsers.
Doesn't look like a browser fingerprint case to me.
Orion is based on Safari, so it may have some awareness of Safari's cookies. Cookies are bits of information about who you are and what you do on websites that get stored locally to your computer.
Firefox has a feature that allows importing data from other browsers. I think other ones can do it automatically.
Privacy has become a very important issue in modern society, with companies and governments constantly abusing their power, more and more people are waking up to the importance of digital privacy.
In this community everyone is welcome to post links and discuss topics related to privacy.
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much thanks to @gary_host_laptop for the logo design :)